JP2013025300A - Electrooptic device, power supplying method of electrooptic device, and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the breakdown of a transistor 140 for making a current pass through a light-emitting element such as an OLED 130.SOLUTION: A pixel circuit 110 includes transistors 124 and 126, and an OLED 130. Of the transistor 124 and the OLED 130 connected in series between voltage variable power supplies, the transistor 124 making a current Ids corresponding to voltage between a gate and a source pass through the OLED 130, and the OLED 130 emits light with luminance corresponding to the current passing between an anode and the source. In the transistor 126 which is diode-connected, a drain (the gate) is connected to a node A, and the source is connected to a feeder line 117 of bias potential Va, so as not to make the voltage of the drain and the source of the transistor 124 exceed a predetermined value.

Description

  The present invention relates to an electro-optical device that prevents destruction of a transistor, a power supply method for the electro-optical device, and an electronic apparatus.

In recent years, various electro-optical devices using light emitting elements such as organic light emitting diode (hereinafter referred to as “OLED”) elements have been proposed. In this electro-optical device, a scanning line and a data line are generally wired on a glass substrate, and a pixel circuit is generally formed corresponding to the intersection of the scanning line and the data line. In addition to the light emitting element, the pixel circuit includes a driving transistor for passing a current through the light emitting element. For this reason, the drive transistor is composed of a thin film transistor.
On the other hand, there is a strong demand for miniaturization and high definition in this type of electro-optical device. Therefore, in recent years, a technique for forming a pixel circuit on a silicon substrate instead of a glass substrate has been proposed (see, for example, Patent Document 1).

JP 2009-152113 A

By the way, in the configuration in which the pixel circuit is formed on the silicon substrate, it is easy to reduce the size of the transistor, but the breakdown voltage of the transistor is lowered. For this reason, it has been pointed out that a voltage exceeding the withstand voltage may be applied to the driving transistor depending on the current flowing through the light emitting element, leading to destruction.
The present invention has been made in view of the above-described circumstances, and one of its purposes is to provide an electro-optical device, a method of supplying power to the electro-optical device, and an electronic apparatus that prevent destruction of a driving transistor that supplies current to a light-emitting element. It is to provide.

  In order to solve the above problems, an electro-optical device according to the present invention includes a pixel circuit including a driving transistor, a light emitting element, and a voltage limiting circuit, and the driving transistor and the light emitting element include a voltage variable power source. The driving transistor causes a current corresponding to a voltage between a gate and a source to flow through the light emitting element, and the light emitting element corresponds to a current flowing between a source and a drain of the driving transistor. Light is emitted with luminance, and the voltage limiting circuit limits the voltage between the drain and source of the driving transistor so as not to exceed a predetermined value. According to the present invention, it is possible to prevent destruction of the driving transistor that supplies current to the light emitting element.

In the present invention, it is preferable that the voltage limiting circuit is a diode having one end connected to a connection point between the driving transistor and the light emitting element and the other end connected to a power supply line having a predetermined potential. In this configuration, it is preferable that the diode is a diode-connected transistor or a diode element. According to this aspect, the diode added to the pixel circuit may be a transistor or a diode element.
In the configuration, the power supply line includes one of the power supplies, a voltage based on a potential at a non-connection point of the two terminals of the light emitting element with the driving transistor, and a threshold voltage of the light emitting element. A potential corresponding to the sum of the threshold voltages of the diodes may be supplied. According to this configuration, even when the power supply voltage is changed, it is possible to limit the voltage between the drain and the source of the driving transistor so as not to exceed a predetermined value in a manner that follows the change.

In the present invention, the pixel circuit is provided corresponding to the intersection of a plurality of scanning lines and a plurality of data lines, and the plurality of scanning lines, the plurality of data lines, and the pixel circuit are: It is preferable that the gate electrode is formed on the same substrate and the potential of the data line is held at the gate of the driving transistor when the scanning line is selected. In this aspect, it is preferable that the first element for obtaining the threshold voltage of the light emitting element and the second element for obtaining the threshold voltage of the diode are respectively formed on the substrate. According to this aspect, the first element and the second element are formed on the same substrate together with the light emitting element and the diode.
In the present invention, the light-emitting element includes a pixel electrode and a common electrode, and the pixel electrode is connected to a power supply line to which a fixed potential is applied via the driving transistor, and the potential of the common electrode is variably set. Therefore, a configuration in which the voltage variable power source is configured is preferable.
In addition to the electro-optical device, the present invention can also be conceptualized as a power supply method for the electro-optical device and an electronic apparatus having the electro-optical device. The electronic device typically includes a display device such as a head-mounted display or an electronic viewfinder.

1 is a perspective view showing an electro-optical device according to an embodiment of the invention. FIG. 4 is a plan view showing an arrangement of each part in the electro-optical device. It is a block diagram which shows the electrical structure of an electro-optical apparatus. It is a figure which shows the pixel circuit in an electro-optical apparatus. It is a figure which shows the bias voltage generation circuit in an electro-optical apparatus. It is a figure which shows operation | movement of an electro-optical apparatus. It is a figure which shows the various electric potential of an electro-optical apparatus. It is a figure which shows the operating point of a drive transistor and OLED. It is a figure which shows the pixel circuit of the electro-optical apparatus (the 1) which concerns on an application and a modification. It is a figure which shows the pixel circuit of the electro-optical apparatus (the 2) which concerns on an application and a modification. It is a figure which shows the structure of the electro-optical apparatus (the 3) which concerns on an application and a modification. 1 is a perspective view showing an HMD using an electro-optical device according to an embodiment. It is a figure which shows the optical structure of HMD. It is a figure which shows the pixel circuit which concerns on a comparative example. It is a figure which shows the operating point of the drive transistor and OLED of a comparative example.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing an electro-optical device 1 according to an embodiment of the present invention.
The electro-optical device 1 shown in this figure includes a micro display 10 that is applied to, for example, a head mounted display (HMD) to display an image. As will be described later, the micro display 10 is an organic EL device in which a plurality of pixel circuits and peripheral circuits for driving the pixel circuits are formed on a silicon substrate, and the pixel circuits include OLEDs.
The micro display 10 is housed in a case 12 that opens corresponding to the arrangement region of the pixel circuits, and one end of an FPC (Flexible Printed Circuits) substrate 14 is connected. A plurality of terminals 16 are provided at the other end of the FPC board 14 and are connected to a circuit module (not shown). The circuit module connected to the terminal 16 also serves as a power source and a control circuit for the micro display 10, and supplies various potentials via the FPC board 14, and also supplies data signals and control signals.

FIG. 2 is a plan view showing the arrangement of each part in the micro display 10, and FIG. 3 is a block diagram showing an electrical configuration in the micro display 10. As shown in FIG. In FIG. 2, for convenience of explanation, the case 12 in FIG. 1 is removed.
In FIG. 2, the display unit 100 has a rectangular shape that is, for example, diagonally 1 inch or less in a plan view and horizontally long in the left-right direction. Referring to FIG. 3 for details, the display unit 100 is provided with m rows of scanning lines 112 along the horizontal direction in the figure, and n columns of data lines 114 along the vertical direction. 112 is provided so as to be electrically insulated from each other. The pixel circuits 110 are arranged in a matrix corresponding to each intersection of the m rows of scanning lines 112 and the n columns of data lines 114.

  m and n are both natural numbers. Further, in order to distinguish the rows of the matrix of the scanning lines 112 and the pixel circuits 110 for convenience, in FIG. 3, the rows may be referred to as 1, 2, 3,... (M−1), m rows in order from the top. is there. Similarly, in order to distinguish the columns of the matrix of the data lines 114 and the pixel circuits 110 for convenience, they may be referred to as 1, 2, 3,..., (N−1), n columns in order from the left in FIG.

The two scanning line driving circuits 140 are respectively arranged on the left and right sides of the display unit 100 as shown in FIG. Specifically, as shown in FIG. 3, the two scanning line driving circuits 140 are configured to drive each of the m rows of scanning lines 112 from both sides.
Each of the scanning line driving circuits 140 is supplied with the same control signal Ctry from the circuit module, and the same scanning signal Gwr ( 1), Gwr (2), Gwr (3),..., Gwr (m-1), Gwr (m) are supplied.
Note that, in this supply, if the delay of the scanning signal does not become a problem, the configuration of only one scanning line driving circuit 140 may be used.

  As shown in FIG. 2, the data line driving circuit 150 is disposed between the connection portion of the FPC board 14 and the display unit 100. As shown in FIG. 3, the image signal Vd and the control signal Ctrx are supplied to the data line driving circuit 150 from the circuit module. In accordance with the control signal Ctrx, the data line driving circuit 150 applies the image signal Vd to the data lines 114 of 1, 2, 3,..., (N−1), the nth column, and the data signals Vd (1), Vd ( 2), Vd (3),..., Vd (n-1), Vd (n).

  As shown in FIG. 2, a bias generation circuit 160 is disposed outside the display unit 100 in the micro display 10, for example, in the lower right corner. The bias generation circuit 160 generates a bias potential Va from the potentials Vel, Vct and the like as shown in FIG. 3 in addition to a logic signal power source, which will be described later. The potentials Vel and Vct are supplied from the circuit module via the FPC board 14. The potentials Vel and Vct are supplied to the display unit 100 together with the bias potential Va from the bias generation circuit 160.

  FIG. 4 is a circuit diagram of the pixel circuit 110. In this figure, the (i + 1) th scanning line 112 adjacent to the i-th row and the i-th row on the lower side, and the (j + 1) -th column adjacent to the j-th column and the j-th column on the right side. A pixel circuit 110 for a total of 4 pixels of 2 × 2 corresponding to the intersection with the data line 114 is shown. Here, i and (i + 1) are symbols for generally indicating the rows in which the pixel circuits 110 are arranged, and are integers of 1 or more and m or less. Similarly, j and (j + 1) are symbols for generally indicating a column in which the pixel circuit 110 is arranged, and are integers of 1 or more and n or less.

  As shown in FIG. 4, each pixel circuit 110 includes p-channel MOS (Metal Oxide Semiconductor) transistors 122, 124, and 126, a capacitor 128, and an OLED 130 that is a light emitting element. Since each pixel circuit 110 has the same configuration, the pixel circuit 110 will be described as being representatively located at i rows and j columns. In the pixel circuit 110 in the i-th row and j-th column, the transistor 122 functions as a switching transistor, and its gate node is connected to the scanning line 112 in the i-th row, while its drain node is the data line in the j-th column. The source node is connected to one end of the capacitor 128 and the gate node of the transistor 124.

The other end of the capacitor 128 is connected together with the source node of the transistor 124 to a power supply line 116 that supplies the potential Vel on the higher power supply side in the pixel circuit 110. The drain node of the transistor 124 is connected to the anode of the OLED 130, the gate node and the drain node of the transistor 126, respectively.
The anode of the OLED 130 is a pixel electrode provided individually for each pixel circuit 110. On the other hand, the cathode of the OLED 130 is a common electrode 118 that covers all of the pixel circuits 110, and is supplied with the potential Vct on the lower power supply side. The OLED 130 is an element in which a light emitting layer made of an organic EL material is sandwiched between an anode and a cathode facing each other, and emits light with a luminance corresponding to a current flowing from the anode toward the cathode.

  On the other hand, the transistors 126 of the voltage limiting circuit are commonly connected across the pixel circuits 110 to a power supply line 117 to which a source node is supplied with a bias potential Va as a predetermined potential. Since the gate node is connected to the drain node, the transistor 126 functions as a diode whose forward direction is from the source node to the drain node.

Note that the pixel circuit 110 in the display portion 100 is formed on a silicon substrate together with the scanning line driving circuit 140, the data line driving circuit 150, and the bias generation circuit 160.
Among these, the scanning signals Gwr (1) to Gwr (m) output from the scanning line driving circuit 140 are logic signals defined at the H or L level. For this reason, the scanning line driving circuit 140 is an assembly of CMOS logic circuits in which the high-order side of the power supply is set to the potential Vdd and the low-order side is set to the potential Vss.
On the other hand, in order to easily form the pixel circuit 110 with a small size and a narrow pitch, the transistors 122, 124, and 126 are all the same p-channel type, for example, and the substrate potential is, for example, the higher potential Vdd.

In FIG. 4, Gwr (i) and Gwr (i + 1) indicate scanning signals supplied to the scanning lines 112 in the i and (i + 1) th rows, respectively, and Vd (j) and Vd (j + 1). ) Indicate data signals supplied to the data lines 114 in the j and (j + 1) th columns, respectively.
For convenience, the gate node of the transistor 124 in the pixel circuit 110 in i row and j column is denoted as g (i, j). A node A is a connection point of the drain node of the transistor 124, the gate node and drain node of the transistor 126, and the anode of the OLED 130.
Note that there may be a case where a capacitor parasitic to the gate node of the transistor 124 can be used for the capacitor 128.

FIG. 5 is a circuit diagram of the bias generation circuit 160.
In this figure, the OLED 130a is a first element for obtaining the threshold voltage Vth_oled of the OLED 130. For this reason, for example, the cathode of the OLED 130a is grounded, and the anode is connected to the power supply line of the higher potential Vdd of the power supply via the resistance element Ra. In this connection state, the resistance value of the resistance element Ra is adjusted so that the voltage between the anode and the cathode of the OLED 130a becomes substantially equal to the threshold voltage Vth_oled of the OLED 130, while keeping the current flowing through the OLED 130a low. Therefore, the voltage output from the operational amplifier 161 of the voltage follower can be regarded as the threshold voltage Vth_oled.
Note that the OLED 130 a has the same structure as the OLED 130, but is provided in an outer region of the display unit 100. The applied voltage of the OLED 130a is substantially the threshold voltage Vth_oled and is a voltage at which light emission starts. Therefore, the OLED 130a does not affect the display on the display unit 100.
In the present embodiment, the ground potential is the lower potential Vss of the logic signal.

  The diode 126a is a second element for acquiring the threshold voltage Vth_diode of the diode-connected transistor 126. For this reason, for example, the cathode of the diode 126a is grounded, and the cathode is connected to, for example, a power supply line of the potential Vel via the resistance element Rb. In this connection state, the resistance element Rb keeps the current flowing through the diode 126a low, and the resistance value so that the voltage between the anode and the cathode of the diode 126a becomes substantially equal to the threshold voltage Vth_diode of the diode-connected transistor 126. Is adjusted. For this reason, the voltage output by the operational amplifier 162 of the voltage follower can be regarded as the threshold voltage Vth_diode. Note that the diode 126a may have a structure in which a transistor having the same size as the transistor 126 is diode-connected.

  The adder circuit 164 including the operational amplifier 163 is supplied with threshold voltages Vth_oled and Vth_diode and a voltage corresponding to the difference between the ground potential and the potential Vct. The adder circuit 164 inverts and outputs these added voltages, and the inverter circuit 166 including the operational amplifier 165 reinverts the inverted added voltage and outputs it as a bias potential Va. For this reason, in the present embodiment, the bias potential Va is a voltage corresponding to the difference between the ground potential and the potential Vct, a threshold value, when the potential Vct that is a non-connection point with the drain node of the transistor 124 in the OLED 130 is used as a reference. This is a potential obtained by adding the voltage Vth_oled and the threshold voltage Vth_diode. The bias potential Va is a potential obtained by adding the threshold voltage Vth_oled and the threshold voltage Vth_diode when the ground potential is used as a reference.

FIG. 6 is a diagram showing a display operation of the micro display 10, and shows an example of waveforms of the scanning signal and the data signal.
As shown in this figure, the scanning signals Gwr (1), Gwr (2), Gwr (3),..., Gwr (m−1), Gwr (m) are horizontally generated by the scanning line driving circuit 140 over each frame. The signals are sequentially selected every scanning period (H) and become L level exclusively.
In this description, a frame means a period required to display an image for one cut (frame) on the micro display 10, and if the vertical scanning frequency is 60 Hz, 16.67 for one cycle. A period of milliseconds. Further, as described above, the scanning line driving circuit 140 uses the high-level side of the power supply as the potential Vdd and the low-level side as the potential Vss, so that the H level of the scanning signal corresponds to the potential Vdd and the L level corresponds to the potential Vss. To do.

  When the i-th scanning line 112 is selected and the scanning signal Gwr (i) changes from the H level to the L level, the j-th data line 114 has a target luminance value of the i-th row and j-th column. A data signal Vd (j) having a corresponding potential is supplied by the data line driving circuit 150.

  When the scanning signal Gwr (i) becomes L level in the pixel circuit 110 in the i row and j column, the transistor 122 is turned on, so that the gate node g (i, j) is electrically connected to the data line 114 in the j column. It becomes a state. Therefore, the potential of the gate node g (i, j) becomes the potential of the data signal Vd (j) as shown by the up arrow in FIG. At this time, the transistor 124 passes a current Ids corresponding to the potential difference between the gate node g (i, j) and the source node, that is, the voltage Vgs, to the OLED 130, while the capacitor 128 has a gate-source voltage Vgs in the transistor 124. Hold.

  When the selection of the i-th scanning line 112 is completed and the scanning signal Gwr (i) becomes H level, the transistor 122 is switched from on to off. Even when the transistor 122 is turned off, the potential of the gate node of the transistor 124 when the transistor 122 is on is held by the capacitor 128 as the gate-source voltage Vgs. For this reason, even if the transistor 122 is turned off, the transistor 124 continues to flow the current corresponding to the voltage held by the capacitor 128 to the OLED 130 until the next i-th scanning line 112 is selected again. Therefore, in the pixel circuit 110 in the i-th row and j-th column, the OLED 130 continues to emit light for a period corresponding to one frame at a luminance corresponding to the potential of the data signal Vd (j) when the i-th row is selected. become.

Note that, in the i-th row, the pixel circuits 110 other than the j-th column also emit light with luminance corresponding to the potential of the data signal supplied to the corresponding data line 114. Although the pixel circuit 110 corresponding to the scanning line 112 in the i-th row is described here, the scanning line 112 is selected in the order of 1, 2, 3,... (M−1), m-th row. As a result, each of the pixel circuits 110 emits light with a luminance corresponding to the target value. Such an operation is repeated for each frame.
In FIG. 6, the potential scale of the data signal Vd (j) and the gate node g (i, j) is expediently expanded rather than the potential scale of the scanning signal which is a logic signal.

Before describing the superiority of the electro-optical device 1 according to the present embodiment, a comparative example of the present embodiment will be described.
FIG. 14 is a diagram illustrating a configuration of a pixel circuit according to a comparative example, and does not include the transistor 126 and the power supply line 117 as compared with FIG.
When the micro display 10 is formed together with the pixel circuit 110 and a peripheral circuit that drives the pixel circuit 110, at least the scanning line driving circuit 140 among the peripheral circuits uses the potentials Vdd and Vss as power sources. For this reason, in the pixel circuit 110 of the comparative example shown in FIG. 14, the potentials Vel and Vct of the power source are made to coincide with the potentials Vdd and Vss, respectively.

FIG. 15 is a diagram showing voltage-current characteristics of the transistor 124 and the OLED 130 in this configuration. As shown in this figure, as the gate-source voltage Vgs of the transistor 124 increases, the current Ids flowing from the source to the drain increases. Note that since the transistor 124 is a p-channel transistor, a larger current Ids flows as the gate node g (i, j) becomes lower than the potential Vel (Vdd).
At this time, as the current Ids increases, the voltage Voled between the anode and the cathode in the OLED 130 increases. Here, the operating point of the transistor 124 and the OLED 130 with respect to the current Ids is indicated by the intersection of both characteristics. The current Ids is defined by the gate-source voltage Vgs in the transistor 124, which is the difference between the potential Vel (Vdd) and the potential of the data signal. The voltage Vgs determined by the data signal tries to define the current Ids flowing through the OLED 130 in the saturation region. However, when the OLED 130 emits light with high brightness, that is, when a large amount of current flows, the operating point B is the anode- Since the voltage Voled between the cathodes is high, the transistor 124 enters the linear region. For this reason, the current defined by the voltage Vgs cannot sufficiently flow through the OLED 130 on the high luminance side. In other words, the OLED 130 cannot sufficiently emit light with the target luminance.

  Therefore, in order to sufficiently supply a current corresponding to the voltage Vgs to the OLED 130 on the high luminance side, as shown in FIG. 7, for example, the pixel circuit 110 is supplied with the potential Vct on the lower side of the power source, that is, the cathode of the OLED 130. It has been considered that the potential Vct is adjusted to be lower than the potential Vss independently of the lower potential Vss of the logic signal that has been shared.

FIG. 8 is a diagram illustrating voltage-current characteristics in a configuration in which the potential Vct is adjusted to be lower than the potential Vss. The transistor 124 is indicated by a solid line, and the OLED 130 in the comparative example is indicated by a broken line.
As shown in this figure, the voltage-current characteristic of the OLED 130 moves to the saturation region in the transistor 124, so that the current defined by the voltage Vgs can flow through the OLED 130 on the high luminance side.

However, when a small current is supplied to the OLED 130 on the low luminance side, the voltage Voled between the anode and the cathode in the OLED 130 decreases, and accordingly, the voltage Vds between the drain and source of the transistor 124 increases accordingly. Further, in this configuration, the power supply voltage (Vdd−Vct) in the pixel circuit 110 is larger than the power supply voltage (Vdd−Vss) of the comparative example.
For this reason, on the low-luminance side, a voltage higher than the withstand voltage may be applied between the drain and the source, and the transistor 124 may be destroyed. In particular, as the pixel circuits 110 are formed with a small size and a narrow pitch, the breakdown voltage of the transistor decreases, which can be a major factor that hinders the miniaturization and high definition of the micro display 10.

On the other hand, the bias potential Va is supplied to the node A, which is a connection point between the drain of the transistor 124 and the anode of the OLED 130 in the present embodiment, via the diode-connected transistor 126. As described above, the bias potential Va is a potential obtained by adding the threshold voltages Vth_oled and Vth_diode with reference to the ground potential, and the component of the threshold voltage Vth_diode is canceled by the diode-connected transistor 126.
For this reason, in the present embodiment, the node A does not fall below the potential obtained by adding the threshold voltage Vth_oled with reference to the ground potential. Therefore, in this embodiment, even if the potential Vct is lower than the potential Vss, the initial power supply voltage (Vdd−Vss), that is, a voltage exceeding a predetermined value, is applied between the drain and source of the transistor 124. Therefore, destruction due to exceeding the withstand voltage is prevented.

  In other words, in this embodiment, when the potential Vct is lower than the potential Vss, the anode-cathode voltage Voled of the OLED 130 is lowered to emit light on the low luminance side, and the node A is based on the ground potential. When the potential falls below the potential obtained by adding the threshold voltage Vth_oled, current starts to flow through the OLED 130 by the bias potential Va. Therefore, as shown by the solid line C in FIG. 8, when viewed from the OLED 130, the anode-cathode voltage Voled does not become lower than Voled (min). The voltage Vds is limited so as not to exceed Vds (max) obtained by subtracting the minimum value Voled (min) from the power supply voltage (Vdd−Vct).

  In the OLED 130, the fact that the voltage between the anode and the cathode does not become lower than the voltage Voled (min) also means that the current flowing from the anode to the cathode does not become a predetermined value or less. For this reason, gradation representation below a certain value cannot be performed on the low luminance side. However, in the configuration in which the display image by the micro display 10 is displayed on the transmission image showing the outside using a half mirror like a head mounted display described later, the gradation expression on the low luminance side is deteriorated. Less likely to be a problem. That is, in an extreme case, even if the display image of the micro display 10 is turned off, a transmitted image is displayed, so that it is difficult to visually recognize the deterioration of gradation expression on the low luminance side.

<Application and modification>
Note that the present invention is not limited to the above-described embodiments, and various applications and modifications as described below are possible, for example. In addition, one or more arbitrarily selected aspects of application / deformation described below can be appropriately combined.

<1. Diode connection>
In the embodiment, in each pixel circuit 110, the transistor 126 is provided between the node A and the power supply line 117 and diode-connected so that the node A side is in the forward direction. However, the present invention is not limited to this. For example, the transistor 126 in FIG. 4 may be replaced with a diode element 136 having an anode connected to the power supply line 117 and a cathode connected to the node A as shown in FIG. That is, in this description, the term “diode” is a concept including a single diode element in addition to a diode-connected transistor.

<2. Light emitting period control transistor>
In the embodiment, the anode of the OLED 130 is directly connected to the drain node of the transistor 124, but as shown in FIG. 10, light emission occurs between the drain node of the transistor 124 and the anode of the OLED 130. A transistor 125 for controlling the period may be provided to be indirectly connected. Specifically, the source node of the transistor 125 is connected to the drain node of the transistor 124, and the drain node of the transistor 125 is connected to the anode of the OLED 130, the drain node and the gate node of the transistor 126, respectively.

For example, a control signal synchronized with the scanning signal is supplied to the gate node of the transistor 125 for each row. For example, control signals Gel (i) and Gel (i + 1) are supplied to the gate nodes of the transistors 125 in the i and (i + 1) -th rows. Accordingly, in the period in which the scanning signal is at the H level, the ratio of the period in which the control signal is at the L level and the transistor 125 is turned on can be made uniform over each row.
Since the equivalent circuit when the transistor 125 is on is FIG. 4 itself, the transistor 124 and the OLED 130 are connected in series between the power supplies, and the transistor 124 depends on the gate-source voltage Vgs. The present embodiment is not different from the above-described embodiment in that the current Ids is supplied to the OLED 130.
In this circuit configuration, in addition to the transistor 124 that supplies current to the OLED 130, the voltage between the source and drain of the transistor 125 that controls the light emission period of the OLED 130 is also protected so as not to exceed the breakdown voltage.

<3. Bias generation circuit>
In the embodiment, the bias generation circuit 160 is formed as a peripheral circuit on the silicon substrate constituting the micro display 10, but the present invention is not limited to this.
Since the bias generation circuit 160 includes analog circuits such as operational amplifiers 161, 162, 163, and 165, if formed on the same silicon substrate, the bias generation circuit 160 is susceptible to noise from the scanning line driving circuit 140 that operates as a logic circuit. On the other hand, since the OLED 130a is provided to acquire the threshold voltage Vth_oled, it is preferable to form it under the same conditions as the OLED 130 as much as possible. Since the diode 126a is also provided for obtaining the threshold voltage Vth_diode, it can be said that it is preferable to form the diode 126a with the same conditions as the transistor 126 as much as possible.

Therefore, as shown in FIG. 11, the OLED 130a and the diode 126a are formed in the region 160a of the micro display 10, and the other circuit elements are configured by an IC circuit 160b mounted on the FPC board 14, for example. Thus, the IC circuit 160 b may supply the bias potential Va to the display unit 100 via the FPC board 14.
Further, circuit elements other than the OLED 130a and the diode 126a may be included in the circuit module described above instead of the IC circuit 160b.

<4. Bias potential>
In the embodiment, the bias potential Va supplied to the power supply line 117 is a potential obtained by adding the threshold voltage Vth_oled and the threshold voltage Vth_diode when the ground potential is used as a reference. However, the present invention is not limited to this. In other words, any structure may be employed as long as the voltage exceeding the breakdown voltage is not applied between the drain and the source of the transistor 124 even if the potential Vct is lower than the potential Vss.

<5. Other>
In the embodiment, the transistors 122, 124, and 126 (125) of the pixel circuit 110 are p-channel type, but may be n-channel type. If the demand for small size and narrow pitch is not strong, a p-channel type and an n-channel type may be mixed.
Further, the light emitting element may be an element other than the OLED. For example, an inorganic light emitting diode or LED (Light Emitting Diode) may be used. In short, any element may be used as long as it emits light with luminance according to the current flowing between the two terminals and the voltage between the terminals changes according to the current to change the voltage between the drain and the source of the transistor 124.
Further, on the higher power supply side of the pixel circuit 110, the potential Vel may be equal to or lower than the higher potential Vdd of the logic signal as shown in FIG.

<Electronic equipment>
Next, a head mounted display to which the micro display 10 according to the embodiment is applied will be described.

FIG. 12 is a diagram showing the external appearance of the head-mounted display, and FIG. 13 is a diagram showing its optical configuration.
First, as shown in FIG. 12, the head mounted display 300 has a temple 31, a bridge 32, and lenses 301R and 301L in the same manner as general glasses. As shown in FIG. 13, the head mounted display 300 includes a left-eye micro display 10L and a right-eye micro display 10R in the vicinity of the bridge 32.
The image display surface of the micro display 10L is arranged on the left side in FIG. Thereby, the display image by the micro display 10L is emitted in the direction of 9 o'clock in the drawing through the optical lens 302L. The half mirror 303L reflects the image displayed by the micro display 10L in the 6 o'clock direction, and transmits light incident from the 12 o'clock direction.
The image display surface of the micro display 10R is arranged on the right side opposite to the micro display 10L. Thereby, the display image by the micro display 10R is emitted in the direction of 3 o'clock in the drawing through the optical lens 302R. The half mirror 303R reflects the image displayed by the micro display 10R in the 6 o'clock direction, and transmits light incident from the 12 o'clock direction.

In this configuration, the wearer of the head-mounted display 300 can see the display image by the micro displays 10L and 10R in a see-through state superimposed on the outside.
Further, in the head mounted display 300, when the left eye image is displayed on the micro display 10L and the right eye image is displayed on the micro display 10R among the binocular images accompanied by parallax, The displayed video can be perceived as if it had a depth or a stereoscopic effect (3D display).

  In addition to the head mounted display 300, the micro display 10 can be applied as an electronic viewfinder in a video camera, an interchangeable lens digital camera, or the like.

DESCRIPTION OF SYMBOLS 1 ... Electro-optical device, 10 ... Micro display, 100 ... Display part, 110 ... Pixel circuit, 112 ... Scan line, 114 ... Data line, 116, 117 ... Feed line, 118 ... Common electrode, 122, 124, 126 ... Transistors, 128, capacitors, 130, OLED, 136, diode elements, 140, scanning line driving circuit, 150, data line driving circuit, 160, bias generation circuit, 300, head mounted display.

In order to solve the above problems, an electro-optical device according to the present invention includes a pixel circuit including a driving transistor, a light emitting element, and a voltage limiting circuit, and the driving transistor and the light emitting element are connected in series between power supplies. The driving transistor causes a current corresponding to a voltage between a gate and a source to flow through the light emitting element, and the light emitting element emits light with a luminance corresponding to a current flowing between a source and a drain of the driving transistor. The voltage limiting circuit limits the voltage between the drain and source of the driving transistor so as not to exceed a predetermined value. According to the present invention, it is possible to prevent destruction of the driving transistor that supplies current to the light emitting element.

Claims (9)

A pixel circuit including a driving transistor, a light emitting element, and a voltage limiting circuit;
The driving transistor and the light emitting element are connected in series between a voltage variable power source,
The driving transistor allows a current corresponding to a voltage between a gate and a source to flow through the light emitting element,
The light emitting element emits light with a luminance corresponding to a current flowing between a source and a drain of the driving transistor,
The electro-optical device, wherein the voltage limiting circuit limits a voltage between a drain and a source of the driving transistor so as not to exceed a predetermined value. The voltage limiting circuit is:
2. The electro-optical device according to claim 1, wherein one end is a diode connected to a connection point between the driving transistor and the light emitting element, and the other end is connected to a power supply line having a predetermined potential. The electro-optical device according to claim 2, wherein the diode is a diode-connected transistor or a diode element. In the feeder line,
One of the power supplies, a potential based on a potential at a non-connection point of the two light emitting elements with respect to the driving transistor, a potential corresponding to a sum of a threshold voltage of the light emitting element and a threshold voltage of the diode The electro-optical device according to claim 2, wherein the electro-optical device is supplied. The pixel circuit is provided corresponding to the intersection of a plurality of scanning lines and a plurality of data lines,
The plurality of scanning lines, the plurality of data lines, and the pixel circuit are formed on the same substrate,
5. The electro-optical device according to claim 1, wherein the potential of the data line is held at a gate of the driving transistor when the scanning line is selected. 6. The electro-optical device according to claim 5, wherein a first element for obtaining a threshold voltage of the light emitting element and a second element for obtaining a threshold voltage of the diode are formed on the substrate. . The light emitting element includes a pixel electrode and a common electrode, and the pixel electrode is connected to a power supply line to which a fixed potential is applied via the driving transistor,
The electro-optical device according to claim 1, wherein the voltage variable power source is configured by variably setting the potential of the common electrode. A pixel circuit including a driving transistor, a light emitting element, and a voltage limiting circuit;
The driving transistor and the light emitting element are connected in series between a variable power source,
A current corresponding to the voltage between the gate and the source of the driving transistor is passed through the light emitting element,
Causing the light emitting element to emit light with a luminance corresponding to a current flowing between two terminals;
A power supply method for an electro-optical device,
The method of supplying power to an electro-optical device, wherein the voltage between the drain and source of the drive transistor is limited so as not to exceed a predetermined value even when the power supply voltage is increased. An electronic apparatus comprising the electro-optical device according to claim 1.

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